Highly Stretchable Polyurethane Porous Membranes with Adjustable Morphology for Advanced Lithium Metal Batteries

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Science

Background:

• Lithium metal batteries (LMBs) require advanced separators for high power density and safety.
• Current separators like polypropylene (PP) have limitations in thermal stability and ionic conductivity.
• Tunable morphology membranes are crucial for mitigating dendrite growth and improving battery performance.

Purpose of the Study:

• To develop a flexible, thermally stable, and ionically conductive porous Polyurethane (PU) membrane for LMBs.
• To investigate the effect of nonsolvent selection on PU membrane morphology and properties.
• To evaluate the performance of the developed PU membrane in Li//Li symmetric and LiFePO4/Li half-cells.

Main Methods:

• Nonsolvent-induced phase separation technique for PU membrane fabrication.
• Combinatorial Density Functional Theory (DFT) and experimental analysis.
• Electrolyte wettability, porosity, mechanical flexibility, thermal stability, and ionic conductivity measurements.
• Electrochemical testing of Li//Li symmetric cells and LiFePO4/Li half-cells.

Main Results:

• Adjustable pore structures (finger-like to sponge-like) achieved by varying nonsolvents.
• PU-EtOH membranes exhibited superior electrolyte wettability (472%), high porosity (75%), and thermal stability (>170°C).
• Elevated ionic conductivity (1.38 mS cm⁻¹) and prolonged lifespan (800 h) in Li//Li symmetric cells compared to PP separators.
• Improved cycling performance in LiFePO4/Li half-cells (115.4 mAh g⁻¹) at 5C rate versus PP separators (104.4 mAh g⁻¹).

Conclusions:

• The developed PU porous membranes offer tunable morphology and enhanced properties for LMBs.
• PU-EtOH membranes significantly improve battery lifespan and cycling performance.
• These membranes show great potential for advancing the efficiency and safety of lithium metal batteries.